HP 8566B CRT focus problem

[jonsikul]

As the title suggests, I am having a problem focusing the CRT on my HP 8566B. When adjusting the focus on the front panel it is like I just need a half a rotation more and then it would focus but the focus screw doesn't allow for that.
Is the CRT just weak?
I just got this machine from an auction without any description on how it works, so I am turning it on for the first time.

[Greybeard]

Check all voltages at the CRT.
Check resistance of all resistors and potentiometer in the focus resistor chain and check solder joints.

May be this helps:
https://www.jvgavila.com/hp8566a.htm